Control device for turbocharged diesel engine

Abstract

An object of the invention is to satisfy various constraints associated with supercharging pressure control even during transitional operation in a turbocharged diesel engine of which a supercharging pressure is actively controllable through operation of an actuator. The control device calculates a steady target value that is a target value of the supercharging pressure during steady operation on the basis of an engine rotation speed and a fuel injection amount, and operates the actuator through feedback control such that an actual supercharging pressure calculated from a signal of a supercharging pressure sensor is brought close to the steady target value. However, when any condition of a plurality of different conditions, which can be satisfied during transitional operation, is satisfied, a transitional target value of the supercharging pressure, suitable for the satisfied condition is calculated in accordance with a calculation rule prepared for each condition. At this time, when there is one transitional target value, the transitional target value is selected, and, when there are a plurality of transitional target values at the same time, one of the transitional target values is selected in accordance with a priority order determined on the basis of an acceleration. A target value of feedback control is changed from the steady target value to the selected transitional target value.

Description

TECHNICAL FIELD[0001]The invention relates to a control device for a turbocharged diesel engine for an automobile and, more particularly, to a control device for a turbocharged diesel engine of which a supercharging pressure is actively controllable through control over a turbine rotation speed with the use of an actuator.BACKGROUND ART[0002]In a diesel engine with a variable displacement turbocharger having a variable nozzle, a supercharging pressure is actively controllable by controlling a turbine rotation speed through an opening degree of the variable nozzle. Therefore, in the thus configured turbocharged diesel engine, a target supercharging pressure is determined on the basis of an engine rotation speed and a fuel injection amount, and the variable nozzle is operated through feedback control such that an actual supercharging pressure that is calculated from a signal of a supercharging pressure sensor becomes the target supercharging pressure.[0003]Incidentally, in control ove...

AI Technical Summary

Benefits of technology

The control device described in this patent text can automatically change the target value of feedback control to a more important constraint when multiple constraints are not met. This allows for optimal supercharging pressure control based on the car's acceleration. The control device does not require complicated functions, as it can adapt to different situations without needing extensive work from a senior R&D personnel.

Problems solved by technology

Incidentally, in control over the turbocharged diesel engine, there are various constraints on hardware or control, associated with an operation amount of the actuator and a state quantity of the engine.

When those constraints are not satisfied, there is a possibility of a breakage of hardware or a decrease in control performance.

When transitional operation in which the engine rotation speed is increasing is also included, man-hours required for adaptation work are enormous.

It is also difficult to adapt the target supercharging pressure without omission on the assumption of all the transitional operation conditions.

Therefore, when the engine is in transitional operation, there is a possibility that part of constraints associated with supercharging pressure control are not satisfied.

One of such constraints is a constraint associated with a reliability guarantee on hardware.

At this time, an exhaust pressure rapidly increases with a steep change in the opening degree of the variable nozzle, so there is a possibility of a breakage of hardware if the exhaust pressure excessively increases.

However, constraints that may not be satisfied during transitional operation are not only a constraint associated with a reliability guarantee on hardware.

The constraints about supercharging pressure control also include a constraint associated with intake sound, a constraint associated with the controllability of an EGR rate, and the like, and those also may not be satisfied during transitional operation.

Speaking of intake sound, there is a possibility of occurrence of a large intake sound that reaches occupant's ears due to a steep change in supercharging pressure.

Speaking of the controllability of the EGR rate, there is a possibility of a decrease in the controllability of the EGR rate due to an excessively small differential pressure between the exhaust pressure and the supercharging pressure.

Because a supercharging pressure control state that can be taken at one time, more specifically, the opening degree of the variable nozzle, which can be taken at one time, is only one, it is not always possible to satisfy all the constraints at the same time.

Images